This application is a National Phase Application (35 USC 371) of PCT/JP99/00547 filed Feb. 9, 1999.
The present invention relates to a magneto-optical recording medium and a magneto-optical recording device.
Conventional techniques in relation to magneto-optical recording media will be described below.
(1) FIG. 1 shows a cross-sectional view of a conventional magneto-optical disk medium, and FIG. 2 illustrates the principle of operation, by reference to a temperature process.
In FIG. 1, reference numeral 1 represents a substrate, 2 a nitride film, 3 a memory layer (TbFeCo), 4 a recording layer (TbDyFeCo), 5 a nitride film, 6 an adhesive layer, 7 a magnet for producing an initialization magnetic field (Hint), and 8 a magnet for producing a bias magnetic field (Hb).
The magneto-optical disk medium shown in these drawings is of overwriting type, in which data are recorded or erased in accordance with the intensity of light. A magnetic layer contains the recording layer 4 and the memory layer 3, which are magnetically coupled with each other. In the magneto-optical disk medium, the recording layer 4 has a high Curie temperature (Tc) [i.e., 280xc2x0 C. (see the upper dotted line of FIG. 2)], and the memory layer 3 has a low Curie temperature (Tc) [i.e., 170xc2x0 C. (see the lower dotted line of FIG. 2)].
When data are to be recorded, a light beam of high intensity is applied to the medium such that the temperatures of the memory layer 3 and the recording layer 4 exceed the Curie temperature of the recording layer 4, whereby the magnetization directions of these layers are reversed to the direction of a bias magnetic field (Hb) (about 200 Oe) (the downward direction in FIGS. 1 and 2).
When data are to be erased, firstly, the magnetization direction of only the recording layer 4 is uniformly reversed to the upward direction in FIGS. 1 and 2 by means of an initialization magnetic field (Hint) (7 kOe). This reverse occurs since the coercive force (Ec) of the recording layer 4 at room temperature is low (i.e., 1 to 2 kOe). Subsequently, a portion of the memory layer 3 at which data are to be erased is irradiated with a light beam of medium intensity, such that the temperature of the memory layer 3 exceeds the Curie temperature Tc of the memory layer. The magnetism of the memory layer 3 temporarily disappears. However, during a cooling process, the memory layer 3 magnetically couples with the recording layer, by means of an exchange coupling force, so that the direction of magnetization of the memory layer 3 becomes upward. In other words, data in the memory layer 3 are erased through magnetic transfer by means of an exchange coupling magnetic field (Hexc).
There has been developed a magneto-optical disk medium including an intermediate layer provided between a recording layer and a memory layer in order to reduce effective exchange coupling force. The internal layer is formed of a magnetic material, such as GdFeCo, which has low perpendicular magnetic anisotropy and enables smooth connection of rotation of micro magnetic domains. Consequently, Hint is reduced to 2.5 kOe, and furthermore, the overall thickness of the magnetic layer can be reduced from 200 nm to 120 nm.
(2) Subsequent progress in development of a magneto-optical disk medium has been in the form of development of a magneto-optical disk medium requiring no initialization magnet.
FIG. 3 shows a cross-sectional view of the conventional magneto-optical disk medium, which contains four layers.
In FIG. 3, reference numeral 11 represents a substrate, 12 a nitride film, 13 a memory layer, 14 a recording layer, 15 a switching layer, 16 an initial magnetization layer, 17 a nitride film, 18 an adhesive layer, and 19 a magnet for producing a bias magnetic field.
The magneto-optical disk medium employs a structure such that an initialization magnet is incorporated into the medium in the form of a magnetic layer. An initialization magnetic layer which has a Curie temperature of 300xc2x0 C. and which is always magnetized in a consistent magnetization direction is provided as the uppermost layer. In order to transmit the effect of initialization to a lower layer in accordance with the intensity of light, the switching layer 15, which has a low Curie temperature (about 150xc2x0 C.), is provided below the initial magnetization layer 16. The disk medium can be operated by use of only the bias magnet 19, since the medium does not require an initialization magnet.
In the magneto-optical disk media described in the above background art techniques (1) and (2), the recording layer 4 and 14 are formed of a metallic magnetic thin film. Each of the disk media employs a Curie point data writing system. The recording layer 4 or 14 of the medium is irradiated with a focused laser beam such that a portion of the layer at which data are to be recorded is heated locally to 280xc2x0 C. (i.e., higher than the Curie temperature of the layer), and a bias magnetic field is applied to thereby promote magnetization reverse. Simultaneously, through exchange coupling, data are transferred to the memory layer. Erasing of data is carried out through combination of irradiation of light and application of an initialization magnetic field [by use of a permanent magnet in the case of the background art technique (1), or by use of an initial magnetization layer in the case of the conventional technique (2)].
An object of the present invention is to provide a magneto-optical recording medium and a magneto-optical recording device which greatly reduce the amount of time and light (electric) energy required for writing and reading of data while maintaining high-density recording and which can reduce the size and energy consumption of the magneto-optical recording device.
To achieve the above object, the present invention provides the following:
[1] A magneto-optical recording medium comprising a recording layer formed of a photoinduced-magnetic material thin film, and a memory layer formed of a ferromagnetic thin film having perpendicular magnetic anisotropy, wherein the recording layer is subjected to photoinduced magnetization in which magnetism is produced directly through irradiation with light under application of a bias magnetic field.
[2] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a magnetic semiconductor (monocrystalline, polycrystalline, or amorphous) thin film.
[3] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a diluted magnetic semiconductor (monocrystalline, polycrystalline, or amorphous) thin film.
[4] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a Group III-V diluted magnetic semiconductor (monocrystalline, polycrystalline, or amorphous) thin film.
[5] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is an organometallic complex (monocrystalline, polycrystalline, or amorphous) thin film.
[6] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a multi-layer structure film containing at least one magnetic semiconductor thin film.
[7] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a multi-layer structure film containing at least one diluted magnetic semiconductor thin film.
[8] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a multi-layer structure film containing at least one Group III-V diluted magnetic semiconductor thin film.
[9] The magneto-optical recording medium described in [1] above, wherein the photoinduced-magnetic material thin film is a multi-layer structure film containing at least one organometallic complex thin film.
[10] The magneto-optical recording medium described in [1] above, wherein the memory layer is a thin film of an alloy or compound containing a transition metal.
[11] The magneto-optical recording medium described in [1] above, wherein the memory layer is a thin film of an alloy or compound containing a rare earth metal.
[12] The magneto-optical recording medium described in [1] above, wherein the memory layer is formed from an Fexe2x80x94Co-based magnetic thin film material.
[13] The magneto-optical recording medium described in [1] above, wherein the memory layer is formed from a Tbxe2x80x94Fexe2x80x94Co-based magnetic thin film material.
[14] A magneto-optical recording device comprising a magneto-optical recording medium which is fixed mounted, which medium comprises a recording layer formed of a photoinduced-magnetic material thin film and a memory layer formed of a ferromagnetic thin film having perpendicular magnetic anisotropy, wherein the recording layer is subjected to photoinduced magnetization in which magnetism is produced directly through irradiation with light.
[15] The magneto-optical recording device described in [14] above, wherein the light irradiation is carried out by means of a low-output semiconductor laser.
[16] The magneto-optical recording device described in [15] above, which further comprises a bias magnetization device.
[17] A magneto-optical recording device comprising a magneto-optical recording medium which assumes a transportable form, which medium comprises a recording layer formed of a photoinduced-magnetic material thin film and a memory layer formed of a ferromagnetic thin film having perpendicular magnetic anisotropy.
[18] The magneto-optical recording device described in [17] above, wherein the light irradiation is carried out by means of a low-output semiconductor laser.
[19] The magneto-optical recording device described in [18] above, which further comprises a bias magnetization device.